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		<title>typeof ecmascripts示例</title>
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		<h1>ECMAScripts typeof 示例</h1>
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			<h2>11.4.3 The typeof Operator </h2>
			The production UnaryExpression : typeof UnaryExpression is evaluated as follows: 
			<h4>1. Evaluate UnaryExpression. </h4>
			<h4>2. If Type(Result(1)) is not Reference, go to step 4. </h4>
			<h4>3. If GetBase(Result(1)) is null, return "undefined". </h4>
			<h4>4. Call GetValue(Result(1)). </h4>
			<h4>5. Return a string determined by Type(Result(4)) 
			   according to the following table: Type Result Undefined "undefined" Null "object" Boolean "boolean" Number "number" String "string" Object (native and doesn't implement [[Call]])
			   "object" Object (native and implements [[Call]]) "function" Object (host) Implementation-dependent</h4>
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